Marsh Fritillaries in South Tyrone

In a survey in 2011, marsh fritillary ‘webs’ had been found at a site in South Tyrone where they had not been recorded for a number of years. Unfortunately a re-survey in 2012 drew a ‘blank’.

Once considered widespread across Europe, the marsh fritillary has declined severely and is a European threatened species. The UK is a European stronghold of the species, but colonies are estimated to be disappearing at over 10% per decade. In Northern Ireland, by 2005 it was only recorded from 8 sites. However, in the last couple of years, several new colonies have been reported in Fermanagh and South Tyrone.

The marsh fritillary is a colonial species found in damp grassland, modified bogs, and boggy or marshy lake shores, where its food plant devil’s bit scabious grows in abundance. Colonies are thought to exist as metapopulations which need a network of sites in a localised area in order to maintain their population which can fluctuate enormously in size from year to year. Populations can decline due to poor weather, unfavourable site conditions and parasitic wasps whose grubs feed inside the caterpillars. Conversely, populations can recover quickly in good years.

Strictly single brooded, the marsh fritillary is on the wing mainly during June and early July. At first adults remain within colonies but once initial egg batches have been laid, females become more mobile and may move from the natal colony. The eggs hatch within a few weeks and the tiny brown caterpillars crowd together and start to feed within a protective silk web which they spin over the food plant. As they moult they will leave this shelter, constructing a new ever larger web on fresh leaves. By the end of August they spin a web close to the ground and are ready to hibernate. They resume feeding in spring, and begin to disperse over their breeding habitat. The pupae form in late April to early May, emerging as adult butterflies three to four weeks later.

In August 2011, as part of the Dungannon & South Tyrone Biodiversity Action Plan, in partnership with Butterfly Conservation, a potential site between Clogher and Fivemiletown, was surveyed for “Marsh Frit Webs”. Although they had not been recorded at this site for a number of years, we were able to find 5 webs in a timed search.

This site was resurveyed in September 2012, and unfortunately no webs were found. It is thought that this site does not have a high density of marsh fritillaries, and it is hoped the lack of webs may have been just a bit of bad luck on the day of the survey. However, the summer we experienced in 2012 had been poor for butterflies in general, and it is believed the marsh fritillary will have suffered just like many other species and numbers will be lower than previous years. However, if we get a couple of good summers, the marsh fritillary population is capable of bouncing back

On the brighter side, in recent years a few new marsh fritillary sites have been discovered in the South Tyrone and Fermanagh areas and with appropriate land management of these sites, the future for this European threatened species is better than it once was.